Fluid flow regulators, particularly regulators used for controlling flow of water in irrigation systems, often control flow of water by controlling the resistance to flow of the water through at least one relatively small flow control channel. Relatively small water flow regulators used for irrigation applications typically provide regulated flow rates between about 10 and 100 liters per hour (l/h) and have components usually formed from plastics by injection molding.
The regulators generally comprise an inlet and an outlet through which water respectively enters and exits the regulator and an elastic diaphragm that prevents water that enters the inlet from flowing directly to the outlet. The inlet and outlet are usually located so that they face each other, with the diaphragm seated on a support shelf and located between them. The diaphragm constrains water that enters the regulator to pass through at least one flow control channel in order for the water to reach the outlet and flow out of the regulator. The diaphragm is responsive to pressure of the entering water, and as pressure of the inlet water increases, the diaphragm undergoes increasing distortion. The diaphragm and at least one flow control channel are configured so that as the distortion increases, the resistance to flow of the at least one flow channel increases substantially proportional to the inlet water pressure. As a result, an amount of water that passes through the regulator is substantially independent of changes in inlet water pressure.
Generally, the at least one flow control channel is an open-faced flow channel defined by a bottom and two sidewalls. Depth of the channel at any location along the channel's length is defined as the height of the sidewalls at the location. In operation, the diaphragm distorts with increasing inlet pressure to cover an increasing length, hereinafter “cover length”, of the open face of the channel. The water is constrained to flow through the covered length of the channel to reach the outlet and as the cover length increases with inlet pressure, the channel resistance to flow of water increases.
In some regulators, as the diaphragm distorts with increasing inlet pressure, the diaphragm first covers the open face of a flow channel at a location, hereinafter a “junction”, at which the channel communicates with the outlet. As the inlet pressure increases, the diaphragm distortion increases and covers the open face of the channel at progressively greater distances from the junction and at locations closer to the support shelf. The cover length of the channel extends from the junction and increases with increasing inlet pressure in a direction away from the outlet towards the support shelf.
However, as distortion of the regulator diaphragm approaches the support shelf, the rate of distortion of the diaphragm with increase in water inlet pressure departs from linearity and decreases with increasing inlet pressure. As a result, rate of increase of cover length of the open face of the at least one flow channel as a function of increase in inlet pressure generally decreases with increasing inlet pressure. If the channel has a uniform cross-section its flow resistance increases at a substantially constant rate with increase in cover length and the regulator must generally be made relatively large so that for a range of inlet pressures for which the regulator is used, flow resistance of the at least one channel increases substantially linearly with inlet pressure.
Smaller regulators have been made in which, as the diaphragm distorts with increasing inlet pressure, the diaphragm first covers the open face of a flow channel near the support shelf and as the inlet pressure increases, the diaphragm distorts to progressively cover regions of the open face of the channel closer to the junction and farther from the support shelf. The cover length of the channel extends from a region near the support shelf and increases with increasing inlet pressure in a direction towards the outlet and away from the support shelf rather than in a direction from the outlet towards the support shelf.
For these regulators, flow channels are configured so that at regions closer to the support shelf, the open face of the channel is closer to the diaphragm than at regions closer to the inlet and the channel is wider and shallower at regions closer to the support shelf than at regions closer to the outlet. The channel gets progressively wider and shallower at distances farther from the inlet and channel resistance to flow per unit length of channel increases with increasing distance, hereafter referred to as “channel distance”, from the inlet. Decreasing channel depth with distance directly decreases cross-section with distance. Increasing channel width would appear to increase channel cross-section with channel distance. However, in operation, the increase in width generally contributes to decreasing channel cross-section with channel distance because at the wider portions of the channel, the diaphragm depresses a greater distance into the channel and “chokes” the cross-section more than at narrower portions of the channel.
Whereas configuring flow control channels with decreasing depth and increasing width enables flow regulators to be made smaller, the relationships between channel depth, width and diaphragm characteristics are relatively complicated and modifying injection molds used to produce the regulators to modify the flow rates they provide is often a tedious and relatively expensive job. Furthermore, because the channels get progressively narrower at distances closer to the junction, i.e. at smaller channel distances, the channels are prone to clogging with dirt and particulate debris carried by the water. In addition, at higher water inlet pressures the operation of the regulators in regulating water flow is relatively sensitive to variations in characteristics, for example elasticity and thickness, of the diaphragm.
U.S. Pat. No. 4,796,810, the disclosure of which is incorporated heroin by reference, describes a rotary irrigation sprinkler comprising a flow control regulator having an elastic diaphragm for controlling flow rate. U.S. Pat. No. 5,279,462 the disclosure of which is incorporated herein by reference, describes a fluid flow control unit having injection molded plastic components that are configured to provide improved assembly using an ultrasonic welding process.